Development of Low Cost Braze Alloys for Aerospace Applications

Abstract

Non-precious metal braze alloys can help lower the cost of brazing, which is a commonly-used joining process in the aerospace industry. A-286, a stainless steel superalloy, and Inconel© 718, a nickel-based superalloy, are both commonly used alloys at Aerojet Rocketdyne. Both alloys were brazed into butt joints using nickel-based braze alloys: AMS 4776, 4777, and 4778. The brazed samples were machined into a modified version of the ASTM E8 subsize specimen samples and tensile tested to compare the strength and calculated elongation of the brazed samples to the base metals’ properties. All of the brazed samples fractured at the joint, and a higher amount of braze alloy on the surface corresponded with a higher strength of the joint. The 718 samples brazed with AMS 4776 and 4778 were not strong enough to be made into tensile samples and the 718 brazed with AMS 4777 reached strengths below 1 ksi due to poor wetting of the braze alloy on the base metal. The average tensile strengths for A-286 brazed with AMS 4776 (A286-76), A286-77, and A286-78 were 30.83 ksi, 93.95 ksi, and 94.91 ksi, respectively. For reference, the base metal had a tensile strength of 145.93 ksi. The average calculated elongations for A286-76, A286-77, and A286-78 were 8.86%, 12.30%, and 15.14%, respectively, and the base metal had a calculated elongation of 58.43%. Metallography along with energy dispersive X-ray spectroscopy revealed interdiffusion regions, grain pinning, voids, and brittle compounds at the center of the joint. Scanning electron microscopy revealed the brazed samples broke in a brittle manner at the joint